Fix Duplicate Step Error

[fa9r]

Describe changes

This PR should fix error messages of the following form: zenml.exceptions.EntityExistsError: Unable to create step '...': A step with this name already exists in the pipeline run with ID '...'.

This would previously be raised if the step run preparation failed after it was already written to DB, causing the error handling code to run into this error when trying to write the failed step run later.

Note that this does not fix the underlying issues that caused the respective errors to be raised, it only fixes the error handling code such that the "correct" error message is now visible in the stack trace.

Pre-requisites

Please ensure you have done the following:

• I have read the CONTRIBUTING.md document.
• If my change requires a change to docs, I have updated the documentation accordingly.
• If I have added an integration, I have updated the integrations table and the corresponding website section.
• I have added tests to cover my changes.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (add details above)